Different non-orthogonal multiple access schemes have been provided that include sparse code multiple access (SCMA), multi-user shared access (MUSA), pattern division multiple access (PDMA), and resource spread multiple access (RSMA) among others. SCMA, for example, employs sparse spreading of information symbols over OFDM sub-carriers for overloading and low complexity decoding. SCMA is non-orthogonal in the sense that content for multiple UEs is transmitted in the same time frequency resource, with the content for different UEs separated through non-orthogonal spreading codes. These schemes are typically used with a fixed channelization scheme. For example, in existing approaches the unit of channelization for SCMA, in particular for grant-free access, is a fixed size contention based transmission unit (CTU). A CTU is defined as a time/frequency/code/pilot symbol combination.
The use of fixed channelization, for example fixed size CTUs, may not result in the best use of resources, for example where an actual amount of data is very small.